This invention relates to forming devices and, more particularly, to a method and apparatus for non-contact extrusion of ductile or moldable materials.
In the manufacture of extrudable articles such as, for example, glass tubes, the tubes are heated to a state of ductility and then shaped to a desired diameter or cross-sectional shape usually by means of molds, i.e., injection molds, by which the glass tube is given the desired extrusion profile. Such a process entails compression of the glass tube, and the internal stress thus created produces varying glass internal material properties which affect the ultimate function of the glass. Thus, where the glass tube is intended for use, after subsequent processing, as a light conductor, the light conductivity can vary, because of the internal stressing, in regions within and throughout the tube to the detriment of the light conducting tube function. Heretofore, the extrusion process as described does not produce as high a degree of uniformity of the product quality as is desirable, resulting in a fairly high scrap rate. Further, the mold, which is in contact with the glass tube, contributes to the non-uniformity through wear, and thus must be replaced more often than is desirable. It is most often necessary to apply a lubricant to insure smooth movement of the work piece within the mold. The desired shaping of the tube profile is, with such a process, extremely limited in just what shape can be imparted to the tube, and, heretofore, has mainly been used to control tube diameter. In the control of tube diameter, it is usual to use a continuous process where the tube is continuously passed vertically, for example, through the mold. The mold thus compresses the tube of the desired diameter as it passes therethrough. Nonetheless, the problems of stress creation in the tube and mold wear still exist, leading to the twin results of a high rate of scrapping and mold wear. It is desirable that the tube be centered on the vertical axis for introduction into the mold. Such centering usually involves, for example, roller elements spaced around the circumference of the tube in contact therewith. The contact of the rollers often results in imparting ovality to the tube, where circularity is most desired.
The present invention is an apparatus and method for extruding ductile tubing into a desired extrusion profile, one of a wide range of profiles, or, alternatively, to producing variations in the cross-sectional configurations of the tube without any physical contact between the mold and the tube, thereby eliminating most of the aforementioned problems.
In greater detail, the apparatus comprises a generally cylindrical device or body member which surrounds the tubing to be shaped. In a preferred embodiment of the invention, the device, which may be of suitable metallic material, such as, for example, steel, has a central bore and is multi-segmented to have a pie shaped configuration. Each segment has a cavity or extrusion cell therein which opens toward the center line of the tube, with the several cell arcs totaling three hundred and sixty degrees. That portion of each cavity or cell immediately adjacent the tube, but spaced therefrom, is filled with a fluid porous member of material such as carbon of the general air bearing type shown in a brochure (not dated) of NEW WAY(copyright) Machine Components, Inc., Aston, Pa. Each segment or cell has an inlet for fluid, such as air, which communicates with the cavity for introduction of the fluid under pressure into the cell and through the porous member onto the work piece, i.e., the ductile tube. The fluid pressure in each segment can be monitored and is adjustable or controllable, preferably by means of a fluid supply and control member which can be manually adjusted or electronically programmed. By means of the pressures in each segment being individually controlled, it is possible, through pressure alone and exclusive of any contact between the device and the tube, to produce a variety of forms or extrusion profiles. Thus, the tube may be converted from a round configuration to a multi-sided configuration such as a square or, for example, a hexagon. For producing substantially straight sides, it is preferable that the porous material have a planar face facing the tube instead of an arc shaped face. The pressure control systems can be programmed to apply fluid under differing pressures to the several segment cells, either simultaneously or sequentially. It is also contemplated that in some instances the fluid can be heated to forestall the possible cooling effect of the fluid as well as to enhance the shaping effect. Thus a single segmented device, hereinafter referred to as a die, can produce substantially precise circular tubes, tapered tubes, oval tubes, square tubes, polygonal tubes, or tubes having desired diametric variations along the length thereof, with a degree of uniformity of quality and precision that materially reduces scrap product and that virtually eliminates die wear.
In other embodiments of the invention, the die may have axially spaced cavities for performing sequential shaping operations either continuously or intermittently on a tube moving axially therethrough. Alternatively, two or more dies may be stacked together to afford the same degree of flexibility or versatility to the invention or a single die may have xe2x80x9cstackedxe2x80x9d cells thereon.
In the various embodiments of the invention, the extruded tube may be monitored, preferably by non-contact monitoring, and the resultant monitoring signals may be fed to a processing unit which controls the fluid pressure control circuit to correct any extrusion errors that might occur.
In operation, the work piece, such as a glass tube, is heated to a ductile state, and passed through the bore of the die or dies. The fluid pressure control system applies fluid, such as air or other suitable fluid, under pressure to the die and through the die to the work piece, with the pressure in the various cells of the die being such as to mold the tube into the desired shape or extrusion profile. As the tube, which, in most cases, is continuously moving, emerges from the die, it is measured or otherwise monitored and any resultant signals thus generated are fed to the fluid pressure control module to vary some or all of the pressures, if necessary. The pressure in one or more of the segments can be varied to correct any extrusion errors.
The apparatus of the invention is also capable of producing centering of the tube on the central axis, for example, concurrently with the extrusion or molding process or prior thereto while controlling a desired profile thereof such as circularity.
The various principles and features of the present invention will be more readily understood from the following detailed description, read in conjunction with the accompanying drawings.